There’s a meme that goes around periodically on Facebook showing Mars, only sized to look as large as the Moon does from Earth. The meme(s) typically argue that when the Earth and Mars hit their smallest distances from one another, Mars will be not only visible to the naked eye as usual, but the same apparent size as the Moon. I’ve always thought these sorts of messages must drive astronomers and scientists absolutely insane, given that the only way Mars would ever look that big from Earth is if every single person living on good ol’ Sol III is about to have a really, really bad day.

It turns out astronomers also make these kind of mistakes. In an excited missive to the Astronomer’s Telegram, Peter Dunsby reported the detection:

[A] very bright optical transient in the region between the Lagoon and Trifid Nebulae based on observations obtained from Cape Town on 20 March 2018, between 01:00 and 03:45 UT. The object was visible throughout the full duration of the observations and not seen when this field was observed previously (08 March 2018). The optical transients is at least first magnitude and is located at the following coordinates: RA (2000): 18h 04m 50s Declination (2000.0): -23d 29m 58s The coordinates are accurate to a few arcseconds. There is no obvious counterpart at this position on the Digital Sky Survey plates. Observations were obtained using an 80mm refractor. The attached URL show the image of this field (2.3 x 1.7 degrees, plate scale of 9 arcseconds per pixel) on 20 March 2018. The optical transient is the brightest star in the field. Further observations are strongly encouraged to establish the nature of this very bright optical transient.

Forty minutes later — undoubtedly a rather long 40 minutes, with some alternating between excitement and then a growing sense of despair — Dunsby posted a follow-up message. In a missive titled “Erratum to ATel #11448,” he notes: “The object reported in ATel 11448 has been identified as Mars. Our sincere apologies for the earlier report and the inconvenience caused.”

While embarrassing for Mr. Dunsby, this is scarcely the first time objects in the solar system have been either misidentified or mistakenly thought to exist. Dwarf planets like Ceres (the first asteroid to be discovered) were originally thought to be planets; Ceres is the only asteroid known to be rounded by its own gravity. Astronomers knew for years that gravitational disturbances in the orbits of Uranus and Neptune could indicate the existence of another planet, but this world, Planet X, was hypothesized to be much larger than the dwarf planet, Pluto, that we eventually found. A hypothetical Planet V between Mars and Jupiter was once theorized as well, with the asteroid belt as the sole remaining evidence of this planet’s existence; this is now thought to be unlikely given the size and distribution of the asteroid belt. Other planets, like Vulcan, a hypothetical planet even closer to the sun than Mercury, were also once expected to exist.

Of course, none of these is quite the same as misidentifying Mars, a planet that’s been known to humanity since ~2000 BC. What can we say? At least Dunsby didn’t make a meme.